The present invention relates generally to a flow coating apparatus, and more specifically to a method and apparatus such as one including a breakaway link for a coating head assembly.
The apparatus and process of the present invention are useful in the printing arts and, more particularly, in the known process of electrophotographic printing.
An electrophotographic printing apparatus can include a charge retentive surface, typically known as a photoreceptor, which is electrostatically charged, and then exposed to a light pattern of an original image to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on the photoreceptor form an electrostatic charge pattern, known as a latent image, conforming to the original image. Contacting the latent image with a finely divided electrostatically attractable powder known as xe2x80x9ctonerxe2x80x9d develops the latent image. Toner is held on the image areas by the electrostatic charge on the photoreceptor surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate or support member (e.g., paper), and the image affixed thereto by fusing the toner image to the paper to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. This process is useful for light lens copying from an original or printing electronically generated or stored originals such as with a raster output scanner (ROS), where a charged surface may-be imagewise discharged in a variety of ways.
Several components in the electrophotographic printing process described above are in the form of polymeric rolls and belts. Fusing rolls, which are used to fix the toner image on a substrate, represent a component that is typically in the form of polymeric rolls and belts. Also included among these components are bias charge rolls (BCRs) and bias transfer rolls (BTRs) that electrostatically charge the photoreceptor. Other forms of polymeric rolls and belts include the pressure or backup roll used with a fusing roll to fix the toner image on a substrate. Another form of a polymeric rolls and belts are donor rolls which transfer oil to the fuser roll that assists in releasing the toner from the fuser roll. A further form of polymeric rolls and belts include intermediate transfer rolls and belts that transfer developed images. Another form of polymeric rolls and belts include photoconductive belts and rolls. Other forms of polymeric rolls and belts include those belts and rolls used in Hybrid Scavangeless Development (HSD) as disclosed in U.S. Pat. No. 4,868,600 to Hays et al. and in U.S. Pat. No. 5,172,170 to Hays et al., the relevant portions thereof incorporated herein by reference. All of these polymeric rolls and belts are typically manufactured by spraying or by dipping
Fuser rolls and belts are examples of polymeric rolls and belts that are particularly difficult to manufacture. The elevated temperatures and pressures of these rolls and the accurate size and finish requirements necessary to insure proper copy quality make their manufacture difficult.
The fusing of the toner image to the paper to form a permanent record of the image is an important part of the xerographic process. Fusing of the toner image is typically done by heat fixation. The heat fixation may be in the form of radiation, conduction, convection, or induction. Most modern xerographic processes adhere the image to the paper by conduction heating the toner image, which is performed by a fusing roll in contact with the toner image. A fusing roll is placed in rolling contact with a backup roll forming a nip therebetween. The paper having the toner image lying thereon is fed between the rolls through the nip. Heat from the fusing roll together with the pressure within the nip between the fuser roll and the backup roll serve to fuse the image to the paper. Heat is typically applied internally within the roll and is transferred through the substrate of the roll onto the periphery of the roll and onto the paper. The rolls typically include a thermally conductive substrate with a surface layer that is also thermally conductive. To assure uniform transfer of the image onto the paper, typically the fuser roll coating is conformable to the paper. For example, the coating may be in the form of a rubber or polymer material, e.g., a fluoroelastomer coating.
Applying fluoroelastomer and other rubber type coatings to fuser roll substrates is fraught with many problems. The coating can be applied to the substrate by a few typical methods. These include dipping of the substrate into a bath of coating solution or spraying the periphery of the substrate with the coating material.
Spraying is a typical method for the manufacture of fluoroelastomer rollers. The spraying process is very slow and costly. Also, the spraying process requires having the coating solution in a form that is very volatile including many volatile organic chemicals. Further, the spraying process is very prone to air pockets or pits forming in the coating. These pits or air pockets in the coating material of the roll result in improper fusing and poor image quality. Because of the nature of the spray process, much of the coating material is lost to the atmosphere requiring an excess amount of the coating material, which can sometimes be costly. Also, the loss of the volatile chemicals can result in expensive containment costs for systems to contain the volatile chemicals as well as increased disposal costs of these materials.
Another typical method for manufacturing fluoroelastomer rollers is to drip material over a horizontally rotating cylinder. With this process a portion of the material adheres to the cylinder and the remainder drips from the cylinder. The amount of material added to the roll is not precisely controlled as the percentage that adheres varies as parameters change over the production run. Also the material forms a wavy surface where the material is poured.
U.S. Pat. No. 5,871,832 discloses a method of coating a substrate, wherein the coating is applied to the substrate by rotating the substrate about its longitudinal axis and applying the coating from an applicator to the substrate in a spiral pattern in a controlled amount so that substantially all the coating that exits the applicator adheres to the substrate. U.S. Pat. No. 5,871,832 is hereby incorporated herein in its entirety.
U.S. Pat. No. 5,871,832 discloses a flow coating process for coating a fuser roll. The method includes first providing a generally cylindrically shaped substrate. The substrate is rotated about a longitudinal axis of the substrate. A fluid coating is applied to the periphery of the substrate in a spiral pattern using a guide to direct the coating onto the periphery of the substrate. After the coating is fully applied, the coating is ground to a precision tolerance. To obtain optimum surface configuration, subsequent operations such as super-finishing or polishing the outer periphery may also be required. This flow coating process is appropriate for generating multi layered printer rolls or belts, for example fuser rolls, e.g., the multi layered fuser roll of U.S. Pat. No. 5,217,837 to Henry et al, the relative portions thereof incorporated herein by reference. The surface condition and the geometry and size of the substrate may require accurate tolerances. Further, the substrate may need preparation to obtain a surface to which the fluid coating may adequately adhere. In embodiments, rolls were constructed using an adhesive coating applied to the substrate. The adhesive coating may be any suitable material, e.g., silane. U.S. Pat. No. 5,219,612 to Bingham and U.S. Pat. No. 5,049,444 to Bingham disclose a specific adhesive layer, the disclosure of which are totally incorporated herein by reference.
A coated fuser roll may be generated that includes coated layers of different materials. For example, a multi layered fuser roll may be used from this process such as a fuser roll described in U.S. Pat. No. 5,217,837 to Henry et al. Such a roll includes a top coating fabricated from a material to obtain optimum release of toner from the roll and a base coat fabricated from a material to obtain optimum thermal transfer. The coating may be applied in a solution with coating additives. Such a solution with approximately 28 percent solids has been found to be effective. The coating may be applied at any satisfactory rate. A rate of 0.002 inches per pass was found to be effective.
In practice, embodiments of this method currently use a coating head assembly that is designed to break in the event of a collision with a roll on the coating conveyor. With the current design, a broken coating head assembly is replaced and rebuilt. Rebuilding the current coating head assembly requires 15 hours per collision.
In accordance with embodiments, a flow coating apparatus has a coating head assembly that incorporates a replaceable breakaway link into the coating head. In the event of a collision, this link will break rather than any other part of the coating head. Repair then only requires the link to be replaced, rather than having to rebuild the coating head assembly. This invention, in embodiments, can reduce coating head repair time from approximately fifteen-hours to rebuild the coating head assembly to approximately three-hours to tool a new link.